Cardiac rhythm management system with prevention of double counting of events

ABSTRACT

A cardiac rhythm management system recognizes patterns of interval durations, distinguishing between events in different heart chambers even though signals associated with those different heart chambers are processed using a commonly shared sensing circuit. A therapy delivery algorithm ignores intervals between cardiac events occurring in different heart chambers when determining a cardiac rate upon which the delivery of therapy is based. This reduces the risk of inappropriate delivery of therapy to the patient. Delayed conduction left ventricular beats are not erroneously recognized as a subsequent right ventricular beat, preventing such short intervals from inappropriately triggering a defibrillation countershock.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.09/801,295, filed on Mar., 7, 2001, now issued as U.S. Pat. No.6,754,534, which is a division of U.S. patent application Ser. No.09/294,725, filed on Apr. 19, 1999, now issued as U.S. Pat. No.6,240,313, the specifications of which are incorporated herein byreference.

TECHNICAL FIELD

This invention relates generally to cardiac rhythm management systemsand particularly, but not by way of limitation, to a cardiac rhythmmanagement system that prevents double counting of one or more ofintrinsic or paced events.

BACKGROUND

When functioning properly, the human heart maintains its own intrinsicrhythm, and is capable of pumping adequate blood throughout the body'scirculatory system. However, some people have irregular cardiac rhythms,referred to as cardiac arrhythmias. Such arrhythmias result indiminished blood circulation. One mode of treating cardiac arrhythmiasuses drug therapy. Drugs are often effective at restoring normal heartrhythms. However, drug therapy is not always effective for treatingarrhythmias of certain patients. For such patients, an alternative modeof treatment is needed. One such alternative mode of treatment includesthe use of a cardiac rhythm management system. Such systems are oftenimplanted in the patient and deliver therapy to the heart.

Cardiac rhythm management systems include, among other things,pacemakers, also referred to as pacers. Pacers deliver timed sequencesof low energy electrical stimuli, called pace pulses, to the heart, suchas via a transvenous leadwire or catheter (referred to as a “lead”)having one or more electrodes disposed in or about the heart. Heartcontractions are initiated in response to such pace pulses (this isreferred to as “capturing” the heart). By properly timing the deliveryof pace pulses, the heart can be induced to contract in proper rhythm,greatly improving its efficiency as a pump. Pacers are often used totreat patients with bradyarrhythmias, that is, hearts that beat tooslowly, or irregularly.

Cardiac rhythm management systems also include cardioverters ordefibrillators that are capable of delivering higher energy electricalstimuli to the heart. Defibrillators are often used to treat patientswith tachyarrhythmias, that is, hearts that beat too quickly. Suchtoo-fast heart rhythms also cause diminished blood circulation becausethe heart isn't allowed sufficient time to fill with blood beforecontracting to expel the blood. Such pumping by the heart isinefficient. A defibrillator is capable of delivering an high energyelectrical stimulus that is sometimes referred to as a defibrillationcountershock. The countershock interrupts the tachyarrhythmia, allowingthe heart to reestablish a normal rhythm for the efficient pumping ofblood. In addition to pacers, cardiac rhythm management systems alsoinclude, among other things, pacer/defibrillators that combine thefunctions of pacers and defibrillators, drug delivery devices, and anyother systems or devices for diagnosing or treating cardiac arrhythmias.

One problem faced by cardiac rhythm management systems is the treatmentof congestive heart failure (also referred to as “CHF”). Congestiveheart failure, which can result from long-term hypertension, is acondition in which the walls of at least one side (e.g., the left side)of the heart become thin. As a result, the left atrium and leftventricle become disproportionately enlarged. The heart muscleassociated with the left atrium and ventricle displays lesscontractility. This decreases cardiac output of blood through thecirculatory system which, in turn, may result in an increased heart rateand less resting time between heartbeats. The heart consumes more energyand oxygen, and its condition typically worsens over a period of time.

As one side of the heart (e.g., the left side) becomesdisproportionately enlarged, the intrinsic electrical heart signals thatcontrol heart rhythm are also affected. Normally, such intrinsic signalsoriginate in the sinoatrial (SA) node in the upper right atrium,traveling through and depolarizing the atrial heart tissue such thatresulting contractions of the right and left atria are triggered. Theintrinsic atrial heart signals are received by the atrioventricular (AV)node which, in turn, triggers a subsequent ventricular intrinsic heartsignal that travels through and depolarizes the ventricular heart tissuesuch that resulting contractions of the right and left ventricles aretriggered substantially simultaneously.

Where one side (e.g., the left side) of the heart has becomedisproportionately enlarged due to congestive heart failure, however,the ventricular intrinsic heart signals may travel through anddepolarize the left side of the heart more slowly than in the right sideof the heart. As a result, the left and right ventricles do not contractsimultaneously, but rather, the left ventricle contracts after the rightventricle. This delay between right ventricular and left ventricularcontractions reduces the pumping efficiency of the heart due to movementof the septal wall between right and left sides of the heart. Congestiveheart failure may also result in an another symptom, that is, an overlylong delay between atrial and ventricular contractions. This too-longdelay between atrial and ventricular contractions also reduces thepumping efficiency of the heart. There is a need to provide congestiveheart failure patients with therapy that improves heart pumpingefficiency.

Conventional cardiac rhythm management techniques, however, aretypically directed toward treating the right side of the heart, whichpumps blood to the lungs. For example, endocardial leads are typicallydesigned to be inserted via the superior vena cava into one or more ofthe right atrium and right ventricle. Because the left side of the heartpumps blood throughout the patient's peripheral circulatory system,pressures are typically higher in the left side of the heart than on theright side of the heart. Because access to the left side of the heart ismore difficult, and because a thrombus forming on a left side lead couldcause a stroke or a myocardial infarction, it is typically verydifficult to chronically implant an endocardial catheter leads directlyinto the left atrium and left ventricle of the heart.

Another problem with treating congestive heart failure patients involvessensing intrinsic heart signals. Cardiac rhythm management devicestypically sense intrinsic atrial and ventricular heart signals, andadjust the therapy being delivered to the heart based at least in parton events detected from these sensed signals or from the delivery of thetherapy itself. Such events are also referred to as “beats,”“activations,” “depolarizations,” or “contractions,” and are sensed viaone or more electrodes located at or near that portion of the heart fromwhich the sensed signals are to be obtained. Atrial depolarizations arealso referred to as “P-waves.” Ventricular depolarizations are alsoreferred to as “QRS complexes,” or “R-waves.” Congestive heart failure,however, may result in a significant delay between right and leftventricular contractions, as discussed above. Such delays not onlydecrease the pumping efficiency of the heart, they may also result inthe sensing of a right ventricular depolarization that is separated intime from a sensed left ventricular depolarization.

In order to properly deliver therapy to the heart based on sensedevents, the cardiac rhythm management system must be able to distinguishbetween sensed right and left ventricular depolarizations that areseparated in time because of delayed conduction through an enlarged leftventricle, and successive depolarizations originating in the same heartchamber that represent successive contractions of the same heartchamber. For example, if the cardiac rhythm management system mistakenlyrecognizes a right ventricular depolarization followed shortly by a leftventricular depolarization as a pair of successive right ventriculardepolarizations, then therapy (such as, for example, a defibrillationcountershock) may be delivered inappropriately, particularly if thisbehavior is sensed repeatedly over several cardiac cycles. Becausedefibrillation countershocks are typically quite painful to the patientand may further irritate the heart, the inappropriate delivery ofdefibrillation countershocks should be avoided, if possible. Similarly,therapy (such as, for example, a pacing stimulus) may be inappropriatelywithheld (i.e., “inhibited”) because the left ventricular depolarizationis mistaken for a subsequent right ventricular depolarization. There isa need for improved sensing and event recognition techniques that reducethe likelihood that left ventricular depolarizations are mistakenlyrecognized as right ventricular depolarizations (or vice-versa) so thatthe cardiac rhythm management system can provide appropriate therapy tothe patient based on sensed events.

SUMMARY

This document discloses, among other things, a cardiac rhythm managementsystem that recognizes patterns of interval durations, allowing it todistinguish between events occurring in different heart chambers, eventhough signals associated with those different heart chambers areprocessed using a commonly shared sensing circuit. The patternrecognition techniques allow the therapy delivery algorithms to ignoreintervals between cardiac events occurring in different heart chamberswhen determining a cardiac rate upon which the delivery of therapy isbased. This reduces the risk of inappropriate delivery of therapy to thepatient. For example, delayed conduction left ventricular beats are noterroneously recognized as a subsequent right ventricular beat,preventing such short intervals from inappropriately triggering adefibrillation countershock.

One aspect of the present system includes a method. The system detectscardiac events. The system obtains a current interval between a currentcardiac event and a previous cardiac event. The system classifies thecurrent interval into at least first and second categories, based on aduration of the current interval. The system determines timing of thedelivery of output energy based on whether a previous interval is in thefirst category and the current interval is in the second category. Thesystem then stores the current interval as the previous interval.

In one embodiment, the system includes a first sensing circuit, adaptedfor being coupled to first and second leads for sensing heart signalsfrom respective first and second heart chambers. A therapy circuit isadapted for being coupled to the first and second leads for deliveringtherapy to the respective first and second heart chambers. A controllercontrols delivery of therapy by the therapy circuit based at least inpart on signals received by the first sensing circuit. The controllerincludes a classification module, classifying previous and currentintervals between cardiac events based on duration. The controller alsoincludes a pattern recognition module, recognizing patterns in thecurrent and previous intervals based on their classification. Thecontroller further includes a therapy delivery control module,controlling delivery of therapy based the intervals between cardiacevents, and ignoring the current interval based on a classification ofthe current and previous intervals. Other aspects of the invention willbe apparent on reading the following detailed description of theinvention and viewing the drawings that form a part thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like numerals describe substantially similar componentsthroughout the several views. Like numerals having different lettersuffixes represent different instances of substantially similarcomponents.

FIG. 1 is a schematic drawing illustrating one embodiment of portions ofa cardiac rhythm management system and an environment in which it isused.

FIG. 2 is a schematic drawing illustrating generally one embodiment ofportions of a cardiac rhythm management device coupled by leads to aheart.

FIG. 3 illustrates generally one possible series of event markersoccurring over a period of time.

FIG. 4 is a state diagram illustrating generally one technique ofcontrolling a counter based on classifications of intervals betweencardiac events.

FIG. 5 is a state diagram illustrating generally another technique ofcontrolling a counter based on classifications of intervals betweencardiac events.

FIG. 6 is a schematic drawing illustrating generally another embodimentof portions of a cardiac rhythm management device providing atrial andbiventricular operation.

FIG. 7 is a schematic drawing illustrating generally a furtherembodiment of portions of a cardiac rhythm management device providingbiatrial and biventricular operation.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that the embodiments may be combined, or that otherembodiments may be utilized and that structural, logical and electricalchanges may be made without departing from the spirit and scope of thepresent invention. The following detailed description is, therefore, notto be taken in a limiting sense, and the scope of the present inventionis defined by the appended claims and their equivalents. In thedrawings, like numerals describe substantially similar componentsthroughout the several views. Like numerals having different lettersuffixes represent different instances of substantially similarcomponents.

FEDERAL SYSTEM OVERVIEW AND EXAMPLES

This document describes, among other things, a cardiac rhythm managementsystem that provides improved sensing and event recognition techniques.The techniques disclosed in this document reduce the likelihood thatleft side depolarizations, for example, are mistakenly recognized asright side depolarizations (or vice-versa). As a result, the presentcardiac rhythm management system can provide more appropriate therapy tothe patient based on sensed events.

FIG. 1 is a schematic drawing illustrating, by way of example, but notby way of limitation, one embodiment of portions of a cardiac rhythmmanagement system 100 and an environment in which it is used. In FIG. 1,system 100 includes an implantable cardiac rhythm management device 105,also referred to as an electronics unit, which is coupled by anintravascular endocardial lead 110, or other lead, to a heart 115 ofpatient 120. System 100 also includes an external or other remoteprogrammer 125 providing wireless communication with device 105 using atelemetry device 130. Catheter lead 110 includes a proximal end 135,which is coupled to device 105, and a distal end 140, which is coupledto one or more portions of heart 115.

FIG. 2 is a schematic drawing illustrating generally, by way of example,but not by way of limitation, one embodiment of portions of device 105coupled by leads 110A-B to heart 115, which includes a right atrium200A, a left atrium 200B, a right ventricle 205A, a left ventricle 205B,and a coronary sinus 220 extending from right atrium 200A. In thisembodiment, right ventricular lead 110A includes one or more electrodes(electrical contacts) disposed in, around, or near right ventricle 205Aof heart 115, such as one or more of a ring, tip, coil, or otherelectrode, for sensing signals or delivering one or more of pacing,defibrillation, countershock, cardioversion, or anti-tachyarrhythmiapacing (ATP) therapy to right ventricle 205A.

In FIG. 2, a left ventricular lead 110B includes one or more electrodesdisposed in, around, or near left ventricle 205B of heart 115, such asone or more of a ring, tip, coil or other electrode, for sensing signalsor delivering one or more of pacing, defibrillation countershock,cardioversion, or anti-tachyarrhythmia pacing therapy to left ventricle205B. Device 105 includes components that are enclosed in ahermetically-sealed can. Additional electrodes may be located on thecan, or on an insulating header, or on other portions of device 105, forproviding one or more of unipolar or bipolar pacing or defibrillationenergy in conjunction with the electrodes disposed on or around heart115. Other forms of electrodes include meshes, patches, and screw-intips which may be applied to endocardial or epicardial portions of heart115 or which may be implanted in other areas of the body to help “steer”electrical currents produced by device 105. The present method andapparatus will work in a variety of configurations and with a variety ofelectrical contacts or “electrodes.”

FIG. 2 illustrates a single-channel embodiment in which at least oneconductor of right ventricular lead 110A is electrically coupled to atleast one conductor of left ventricular lead 110B, such that electrodesassociated with right ventricle 205A and left ventricle 205B share acommon ventricular sensing circuit 210 and a common ventricular therapycircuit 215. Variations of the illustrated single-channel embodimentinclude other channels (e.g., associated with other heart chambers), butat least one of the channels is coupled to electrodes at two differentlocations, such as within two different chambers of heart 115. In oneexample, leads 110A-B are implemented as a single lead that isbifurcated to allow disposition of electrodes at different locations,such as associated with two different chambers of heart 115. In anotherexample, leads 110A and 110B are separate leads that are received atreceptacles at a header portion of device 105, but at least oneconductor of lead 110A is electrically coupled to at least one conductorof lead 110B within the header or elsewhere in device 105, or using anadapter located in the lead 110. In one embodiment, right ventricularlead 110A is an intravascular endocardial lead with an electrodedisposed near the apex of right ventricle 205A, and left ventricularlead 110B is an epicardial lead with a screw-in or other electrodeassociated with left ventricle 205B. In another embodiment, however,left ventricular lead 110B is an intravascular endocardial lead thatintroduced into the coronary sinus 220. This lead 110B is then extendedinto the great cardiac vein such that an intravascular electrode isassociated with tissue of left ventricle 205B.

In FIG. 2, device 105 also includes a communication interface 220, suchas a circuit for communicating with remote programmer 125 via telemetrydevice 130. Ventricular sensing circuit 210 receives intrinsic heartsignals from leads 110A-B, but because the conductors of leads 110A-Bare electrically intercoupled, sensing circuit 210 receives no otherindependent information regarding the chamber in which the sensedsignals originated. Controller 225 includes one or more of hardwaremodules, software modules, firmware modules, or other components orexecutable instructions. Various modules are illustrated conceptually inFIG. 2 as blocks, but some of these modules are understood to includeone or more sequences of steps carried out on controller 225, such as byexecuting stored microcode or other instructions.

Controller 225 receives one or more signals from ventricular sensingcircuit 210 that include information about sensed ventricular events.Based on sensed events, among other things, portions of the algorithmsexecuted by controller 225 determine timing of delivering pacing,defibrillation, or other therapy, and also determine other therapyparameters. Accordingly, controller 225 provides control signals totherapy circuit 215 for controlling the delivery of output energy orother therapy to heart 115. Such therapy includes, for example, pacingenergy pulses delivered simultaneously to right and left ventricles205A-B. In another example, such therapy includescardioversion/defibrillation/countershock energy pulses deliveredsimultaneously to right and left ventricles 205A-B.

Controller 225 computes intervals between cardiac events, such as pacedor sensed ventricular (right or left) events. A memory location, such assecond register 235, stores a current ventricular interval. The currentventricular interval is the time between the most recently detectedventricular event, V_(n), and an immediately preceding ventricularevent, V_(n−1). It is unknown whether such ventricular events areassociated with right ventricle 205A or left ventricle 205B, becauseventricular sensing circuit 210 interfaces to these chambers byelectrodes that are electrically intercoupled. A memory location, suchas first register 230, stores a previous ventricular interval. Theprevious ventricular interval is the time between the ventricular event,V_(n−1), and an associated immediately preceding ventricular event,V_(n−2).

Pattern recognition module 240 classifies each of the previous andcurrent intervals based on their respective durations. The patternrecognition module 240 also evaluates each pair of previous and current(“previous-current”) intervals based on the assigned classification, asdiscussed below. Pattern recognition module 240 increments, decrements,and holds a count value stored in up-down counter 245 (also referred toas a pattern counter 245) based on the evaluation of the classificationassigned to the intervals. The algorithm carried out within controller325 bases the delivery of output energy by therapy circuit 215 on, amongother things, the count value of counter 245.

Controller 225 also includes a therapy delivery control module 250,which executes a therapy delivery algorithm for determining the timingand other parameters of pacing therapy, anti-tachyarrhythmia therapysuch as defibrillation countershocks or anti-tachyarrhythmia pacing(ATP), or other therapy. In one embodiment, therapy delivery module 250includes a tachyarrhythmia event counter 255 that counts short cardiacintervals for diagnosing tachyarrhythmias and triggering appropriateanti-tachyarrhythmia therapy.

FIG. 3 illustrates generally, by way of example, but not by way oflimitation, one possible series of event markers occurring over a periodof time. These markers represent an example of the occurrence of onepossible set of events sensed by ventricular sensing circuit 210 ordelivered by ventricular therapy circuit 215 over a period of time. Eachevent markers is described according to characteristics of the event itrepresents. In one example, an intrinsic right ventriculardepolarization 300A at time t₁ results from intrinsic heart signalsconducted from the right atrium, through the atrio-ventricular node, theseptum, and the right ventricle. Sensed right ventricular depolarization300A initiates a post-sense refractory period 305A, during which timesensed signals are ignored, because it is unlikely that such signalsrepresent another ventricular depolarization during that time. Thepost-sense refractory period 305A expires at time t₂, after which timesensed signals are no longer ignored by device 105.

At time t₃, another intrinsic right ventricular depolarization 300Bresults from intrinsic heart signals conducted from the right atrium,through the atrio-ventricular node, the septum, and the right ventricle.Right ventricular depolarization 300B initiates another post-senserefractory period 305B, which expires at time t₄. In a patient withcongestive heart failure, however, the same intrinsic signal thatresulted in right ventricular depolarization 300B is conducted moreslowly along the left side of the heart because the left side of theheart is enlarged. This results in a delayed left ventriculardepolarization 310A at time t₅. In many patients, the delay inconduction in left ventricle 205B is long enough that the delayed leftventricular depolarization 310A occurs after expiration of thepost-sense ventricular refractory period 305B. In a single-channelsystem, where right and left ventricular leads 110A-B, are tiedtogether, it is possible that the delayed left ventriculardepolarization 310A is mistaken for another occurrence of a rightventricular depolarization. In such a case, if device 105 erroneouslycomputes ventricular heart rate based on the interval t₅-t₃, thecomputed heart rate would be extremely fast. The interval t₅-t₃ does notcorrespond to an interval between ventricular events occurring in thesame chamber (e.g., the right ventricle), but rather, to ventricularevents occurring in different chambers (e.g., the right and leftventricles).

This pattern of events can occur repeatedly, as illustrated by thesubsequent event markers 300C, 310B, 300D, and 310C in FIG. 3. In such acase, intervals t₉-t₇ and t₁₃-t₁₁ also provide erroneous indications ofextremely fast ventricular heart rates. These erroneous indications of afast ventricular heart rate can result in, among other things, theinappropriate delivery of anti-tachyarrhythmia therapy. There is a needfor finding some basis of distinguishing between erroneously indicatedfast ventricular rates, and actual high ventricular rates. This need isparticularly strong in a single channel device in which conductors andsense amplifiers are shared between left and right ventricles. In such asingle-channel device, the same sense amplifier detects events from morethan one chamber, and intervals between events in different chamber maybe mistaken for events occurring in the same chamber.

Furthermore, device 105 should recognize and respond to the problempattern of FIG. 3 without increasing the duration of the post-senserefractory periods 305. Extending the post-sense refractory periods 305so that they are long enough to encompass the expected delayed leftventricular contractions would also blind device 105, for a longerperiod of time, to successive right ventricular senses that actually dooccur at high rates. Thus, extending the post-sense refractory periods305 may increase the time before a tachyarrhythmia is recognized andtreated, or it may result in a failure to recognize and properly treatthe tachyarrhythmia altogether.

One aspect of the present system recognizes a pattern among thedurations of intervals between cardiac events. The system uses thispattern of interval durations to distinguish intervals concluded bydelayed left ventricular contractions 310 from intervals concluded byactual right ventricular contractions 300. This allows device 105 toaccurately determine heart rate based on events occurring in the sameheart chamber, even when using a shared sensing circuit 210 that detectsevents associated with more than one heart chamber.

First, pattern recognition module 240 classifies intervals betweencardiac events into at least two categories based on duration. In oneexample, each cardiac interval is compared to a predetermined comparisonvalue T₁ such as, for example, T₁=500 milliseconds, or other suitablevalue. Intervals shorter than T₁ are classified as “short,” andintervals longer than T₁ are classified as “long”. In one embodiment,intervals equal to T₁ are included in the “short” category, however,such intervals could alternatively be included in the “long” category.In one embodiment, the value of T₁ is user programmable, allowingadjustment of long and short classifications to suit the needs of theparticular patient.

Second, pattern recognition module 240 uses the interval classificationsto distinguish successive events occurring in the same chamber fromsuccessive events occurring in different chambers, so that therapydelivery algorithms do not erroneously consider intervals between eventsoccurring in different heart chambers as being indicative of heart ratein a single heart chamber. In one embodiment, classifications of pairsof previous and current intervals (also referred to as previous-currentinterval pairs) are used to remove such erroneous intervals fromconsideration by the therapy delivery algorithms.

In one example, classifications of previous and current intervals arepaired inputs used to increment, decrement, or hold the count of up-downcounter 245. FIG. 4 is a state diagram illustrating generally, by way ofexample, but not by way of limitation, one technique of controllingcounter 245 based on the classifications of previous and currentintervals. FIG. 4 illustrates the states of the previous interval, i.e.,a long state 400 and a short state 405. Transitions between these statesare indicated by arrows, with corresponding text describing how counter245 is affected during such transitions.

Transition 410 illustrates how counter 245 is affected if the previousinterval is long and the current interval is short. For such along-then-short previous-current interval pair, if the count valuestored in counter 245 is less than a predetermined value C₁, such as,for example, C₁=3, then counter 245 is incremented. Otherwise, the countvalue stored in counter 245 is equal to the predetermined value C₁, inwhich case the current interval is disregarded by the therapy deliveryalgorithm. Stated differently, pattern recognition module 240 recognizesa long interval followed by a short interval. If a sufficient amount oflong-then-short previous-current interval pairs are detected over aperiod of time, pattern recognition module 240 deems the current shortinterval as resulting not from same chamber depolarizations, but rather,as resulting from depolarizations associated with different chambers.Such a short interval is inappropriate for computing a heart rate uponwhich therapy delivery is based, because it does not represent a timebetween cardiac events occurring in the same heart chamber.

Transition 415 illustrates how counter 245 is affected if the previousand current intervals are both short. For such a short-then-shortprevious-current interval pair, if the count value stored in counter 245is greater than a predetermined value C₂, such as, for example, C₂=0,then counter 245 is decremented. Otherwise, the count value stored incounter 245 is equal to the predetermined value C₂, and the count valueof counter 245 is not modified.

Transition 420 illustrates how counter 245 is affected if the previousand current intervals are both long. For such a long-then-longprevious-current interval pair, if the count value stored in counter 245is greater than a predetermined value C₂, such as, for example, C₂=0,then counter 245 is decremented. Otherwise, the count value stored incounter 245 is equal to the predetermined value C₂, and the count valueof counter 245 is not modified.

Transition 425 illustrates how counter 245 is affected if the previousinterval is short and the current interval is long. For such ashort-then-long previous-current interval pair, the count value storedin counter 245 is not changed.

Referring again to FIG. 3, in a congestive heart failure patient, thereis loss of synchrony between the right and left ventriculardepolarizations, due to enlargement of the left side of the heart, whichresults in delayed conduction of signals through the left side of theheart. As a result, the same ventricular depolarization wavefronttravels more slowly through the left side of the heart than through theright side of the heart. This results in the detection of rightventricular depolarization 300B followed by an independent delayedconduction left ventricular depolarization 310A. If each intervalconcluded by a delayed conduction left ventricular depolarization 310(e.g., t₅-t₃, t₉-t₇, t₁₃-t₁₁) is shorter than or equal to (or,alternatively, shorter than) T₁, then each such interval will beclassified as short. If each interval concluded by a right ventriculardepolarization 300 (e.g., t₇-t₅, t₁₁-t₉) is longer than (oralternatively, longer than or equal to) T₁, then each such interval willbe classified as long.

By choosing the appropriate value of T₁, it is possible to discriminatebetween intervals concluded by right ventricular depolarizations 300 andintervals concluded by left ventricular depolarizations 310, becausethey are classified as long and short, respectively. Furtherdiscrimination is provided by noting that a delayed conduction leftventricular depolarization is manifested by a short interval thatfollows a long interval. Such a pattern is recognized by patternrecognition module 240. As described above with respect to FIG. 4, acounter is used to recognize the occurrence of this repeating pattern oflong-then-short intervals. Pattern recognition module 240 increments thecounter for a long-then-short previous-current interval pair, decrementsthe counter for a long-then-long or a short-then-short previous-currentinterval pair, and holds the count value for a short-then-longprevious-current interval pair. By so doing, pattern recognition module240 is capable of recognizing a number of long-then-shortprevious-current interval pairs occurring closely in time, beforedirecting the therapy delivery algorithm to ignore the short currentinterval. However, it is understood that count value C₁ is programmable.For C₁=1 a single long-then-short previous-current interval pair is allthat is needed to direct the therapy delivery algorithm to ignore theshort current interval. For larger values of C₁, more than onelong-then-short previous-current interval pair is required to ignore theshort current interval. By using an up-down counter 245 and C₁>1, atleast two successive long-then-short previous-current interval pairs isrequired to ignore the short current interval.

Controller 225 includes a therapy delivery control module 250, whichexecutes a therapy delivery algorithm. In one embodiment, the therapydelivery algorithm delivers some form of anti-tachyarrhythmia therapy ifa predetermined number of short intervals occur during a time period. Itis understood the criteria used to classify the intervals as short fortriggering delivery of anti-tachyarrhythmia therapy may be differentfrom the criteria used for the long/short pattern recognition describedabove. In one embodiment, however, intervals are classified as short fordetermining whether anti-tachyarrhythmia therapy should be deliveredusing the same criteria that result in a short classification for thepattern recognition described with respect to FIG. 4.

In one example, the therapy delivery control module 250 includes atachyarrhythmia event counter 255, such as an up-down counter, forcounting the occurrences of short intervals. Thus, if the currentinterval is short, counter 255 is incremented, but if the currentinterval is not short, counter 255 is decremented or held at itsprevious value. If counter 255 reaches a value indicating that asufficient number of short intervals have been detected during a desiredtime period, then anti-tachyarrhythmia therapy is delivered to thepatient.

Using the present system, however, if the current interval is short, butis preceded by a sufficient number of long-then-short previous-currentinterval pairs during a period of time (such that the count value ofcounter 245 is equal to C₁), then the current interval is ignored by thetherapy delivery algorithm being executed by therapy delivery controlmodule 250, such as by not incrementing the tachyarrhythmia eventcounter 255. In another embodiment, the current interval is similarlyignored by portions of the therapy delivery algorithm that control thedelivery of bradyarrhythmia therapy pacing energy pulses.

FIG. 5 is a state diagram, similar to FIG. 4, illustrating generally, byway of example, but not by way of limitation, another technique ofcontrolling counter 245 based on the classifications of previous andcurrent intervals. As illustrated in FIG. 5, more than twoclassifications may be used. In one embodiment, intervals are classifiedas either long, medium, or short by comparing the interval topredetermined comparison values T₁ and T₂, where T₂>T₁. Intervalsshorter than T₁ are classified as “short,” intervals longer than T₂ areclassified as “long,” and intervals longer than T₁ but shorter than T₂are classified as “medium.” In one embodiment, intervals equal to T₁ areincluded in the “short” category and intervals equal to T₂ are includedin the “long” category, however, such intervals could alternatively beincluded in the “medium” category. In one embodiment, the values of T₁and T₂ are user programmable, allowing adjustment of long and shortclassifications to suit the needs of the particular patient.

FIG. 5 illustrates the states of the previous interval, i.e., a longstate 400, a short state 405, and a medium state 500. Transitionsbetween these states are indicated by arrows, with corresponding textdescribing how counter 245 is affected during such transitions.Transitions involving only the long state 400 or short state 405 are asdescribed above with respect to FIG. 4. Transition 505 illustrates howcounter 245 is affected for both long-then-medium and medium-then-longprevious-current interval pairs. Transition 510 illustrates how counter245 is affected for both medium-then-short and short-then-mediumprevious-current interval pairs. Transition 515 illustrates how counter245 is affected for a medium-then medium previous-current interval pair.For each of transitions 505, 510, and 515, if the count value stored incounter 245 is greater than a predetermined value C₂, such as, forexample, C₂=0, then counter 245 is decremented. Otherwise, the countvalue stored in counter 245 is equal to the predetermined value C₂, andthe count value of counter 245 is not modified.

FIG. 6 is a schematic drawing, similar to FIG. 2, illustratinggenerally, by way of example, but not by way of limitation, anotherembodiment of portions of device 105 including an atrial sensing circuit600 and an atrial therapy circuit 605 coupled by lead 610 to rightatrium 200A for sensing signals or delivering stimulations orcountershocks. FIG. 6 illustrates that the techniques described abovecan provide cardiac rhythm management therapy in first and second heartchambers (e.g., right atrium 200A and right ventricle 205A), operatingin any of the conventional dual-chamber pacing modes, in combinationwith sensing and therapy in a third heart chamber (e.g., left ventricle205B) provided by circuits shared between the second and third heartchambers. Such pacing therapy may also be combined withanti-tachyarrhythmia therapy (such as anti-tachyarrhythmia pacing or acountershock) delivered to right atrium 200A, right ventricle 205A, andleft ventricle 205B.

FIG. 7 is a schematic drawing, similar to FIG. 6, illustratinggenerally, by way of example, but not by way of limitation, anotherembodiment of portions of device 105 including an atrial sensing circuit600 and atrial therapy circuit 605 that are shared between regionsassociated with right atrium 200A and left atrium 200B, to which theyare coupled by electrically interconnected leads 610A and 610B,respectively. FIG. 7 illustrates that the techniques described above canalso provide cardiac rhythm management therapy in first and second heartchambers (e.g., right atrium 200A and right ventricle 205A) operating inany of the conventional dual-chamber pacing modes, in combination withsensing and therapy in third and fourth heart chambers (e.g., leftventricle 205B and left atrium 200B) provided by circuits shared betweenthe first and fourth (e.g., atria 200) heart chambers and the second andthird (e.g., ventricles 205) heart chambers. Such pacing therapy may becombined with anti-tachyarrhythmia therapy (such as anti-tachyarrhythmiapacing or a countershock) delivered to any of the heart chambers. InFIG. 7, the techniques discussed above for distinguishing betweenventricular events using pattern recognition are also used fordistinguishing between atrial events. In this embodiment, device 105includes a separate atrial pattern recognition module 700, withassociated third register 705, fourth register 710, and atrial patterncounter 715, which operate as described above with respect to theventricles. Similarly, therapy delivery control module 250 includes anatrial tachy event counter 720 that ignores the current interval when sodirected by atrial pattern recognition module 700, as described abovefor the ventricles.

CONCLUSION

The above-described system provides, among other things, cardiac rhythmmanagement system that recognizes patterns of interval durations,allowing it to distinguish between events occurring in different heartchambers, even though signals associated with those different heartchambers are processed using a commonly shared sensing circuit. Thepattern recognition techniques allow the therapy delivery algorithms toignore intervals between cardiac events occurring in different heartchambers when determining a cardiac rate upon which the delivery oftherapy is based. This reduces the risk of inappropriate delivery oftherapy to the patient. For example, delayed conduction left ventricularbeats are not erroneously recognized as a subsequent right ventricularbeat, preventing such short intervals from inappropriately triggering adefibrillation countershock.

The above description is intended to be illustrative, and notrestrictive. Many other embodiments will be apparent to those of skillin the art upon reviewing the above description. For example, thephysiology of the heart may result in a right ventricular contractionthat is delayed from a left ventricular contraction. By interchangingthe roles of the right and left ventricular events in FIG. 3, forexample, the above-described techniques can still be used to distinguishbetween intervals concluded by right ventricular events and intervalsconcluded by left ventricular events. Also, FIG. 3 was describedprimarily in terms of sensed right ventricular events 300. However, suchright ventricular events 300 could also include paced events, such aswhere a pace is simultaneously delivered to the ventricles 205, butfails to capture left ventricle 205B, resulting in a delayed conductionsensed left ventricular event 310.

Moreover, although the therapy delivery algorithms were described aboveas ignoring the current cardiac interval if the pattern recognitioncriteria are met, in an alternate embodiment, ignoring the currentcardiac interval includes adding the time of the current cardiacinterval to the time of the next cardiac interval. For example, if theperiod t₅-t₃ of FIG. 3 is ignored, in one embodiment, the time t₅-t₃ isadded to the time t₇-t₅ in computing the duration of the next cardiacinterval. This recomputation of the next cardiac interval can be used,among other things, by the therapy delivery control module for computinga heart rate upon which therapy delivery is based. For example, in oneembodiment, when the current interval is t₉-t₇, a recomputed previousinterval of t₇-t₃ is used rather than a previous interval of t₇-t₅, asdescribed above.

Also, the pattern recognition was described above as classifying thecurrent interval, with the interval retaining its same classificationwhen the current interval is then stored as the previous interval.Alternatively, a separate classification is performed for the previousinterval, allowing for the possibility of different intervalclassification criteria for the previous interval, and reclassificationof the current interval when it is stored as the previous interval. Suchreclassification may be particularly useful in an embodiment using arecomputed previous interval, as described in the previous paragraph.

Moreover, the controller 225 was described above as storing the intervalduration in the first register 230 and second register 235. However, itis understood that in an alternate embodiment, other information isstored in the first register 230 and second register 235, such as a coderepresenting the classification (e.g., long, short, or medium) of theinterval. Also, first register 230 and second register 235 could becombined with each other, or with another memory location; they areillustrated separately for conceptual clarity.

Furthermore, the pattern recognition techniques were described above,for illustrative purposes, using an algorithmic approach. It isunderstood that the same techniques could alternatively be implementedusing a neural network. The scope of the invention should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

1. A method including: (a) detecting cardiac events using a firstsensing circuit for sensing heart signals from first and second heartchambers, wherein the first and second heart chambers are both atria, orwherein the first and second heart chambers are both ventricles; (b)obtaining intervals between cardiac events associated with the first andsecond heart chambers; (c) pairing successive intervals intofirst-second interval pairs; (d) classifying the intervals, according totheir duration, into at least first and second categories; (e)recognizing patterns in the first and second intervals based on theirclassification, the recognizing patterns comprising counting, among afirst predetermined number of most recent first-second interval pairs, asecond predetermined number of one or more first-second interval pairsin which the first interval is in the first category and the secondinterval is in the second category; and (f) determining timing ofdelivery of output energy based on (e).
 2. The method of claim 1, inwhich (a) includes detecting events in one of (1) right and leftventricles, or (2) right and left atria.
 3. The method of claim 1, inwhich (d) includes: classifying the first interval of the first-secondinterval pair into the first category if it is longer than a firstduration, and classifying the first interval into the second category ifit is shorter than the first duration; and classifying the secondinterval of the first-second interval pair into the first category if itis longer than a second duration, and classifying the second intervalinto the second category if it is shorter than the second duration. 4.The method of claim 1, in which the first and second durations areapproximately equal.
 5. The method of claim 3, including at least one of(1) classifying the first interval into the first category if it isequal to the first duration, or (2) classifying the second interval intothe first category if it is equal to the second duration.
 6. The methodof claim 3, including at least one of (1) classifying the first intervalinto the second category if it is equal to the first duration, or (2)classifying the second interval into the second category if it is equalto the second duration.
 7. A system, including: a first sensing circuit,for sensing heart signals from respective first and second heartchambers, wherein the first and second heart chambers are both atria, orwherein the first and second heart chambers are both ventricles; atherapy circuit, for delivering therapy to the respective first andsecond heart chambers; and a controller, controlling delivery of therapyby the therapy circuit based at least in part on signals received by thefirst sensing circuit, the controller including: a classificationmodule, classifying previous and current intervals between cardiacevents of the first and second heart chambers according to theirduration; a pattern recognition module, recognizing patterns in thecurrent and previous intervals based on their classification; and atherapy delivery control module, controlling timing of delivery oftherapy based on the intervals between cardiac events.
 8. The system ofclaim 7, in which the first and second chambers include respective rightand left ventricles.
 9. The system of claim 7, in which the first andsecond chambers include respective right and left atria.
 10. The systemof claim 7, further including a first lead, adapted to be coupled to thefirst heart chamber and a second lead adapted to be coupled to thesecond heart chamber.
 11. The system of claim 7, further including aremote programmer.
 12. The system of claim 11, in which the remoteprogrammer provides parameters to the classification module foradjusting the classification of the intervals.
 13. A system, including:a first sensing circuit, for sensing heart signals from respective firstand second heart chambers, wherein the first and second heart chambersare both atria, or wherein the first and second heart chambers are bothventricles; a therapy circuit, for delivering therapy to the respectivefirst and second heart chambers; and a controller, controlling deliveryof therapy by the therapy circuit based at least in part on signalsreceived by the first sensing circuit, the controller including: meansfor classifying previous and current intervals between cardiac events ofthe first and second heart chambers according to their duration; meansfor recognizing patterns in the current and previous intervals based ontheir classification; and a therapy delivery control module, controllingtiming of delivery of therapy based on the intervals between cardiacevents.
 14. The system of claim 13, in which the first and secondchambers include respective right and left ventricles.
 15. The system ofclaim 13, in which the first and second chambers include respectiveright and left atria.
 16. The system of claim 13, further including afirst lead, adapted to be coupled to the first heart chamber and asecond lead adapted to be coupled to the second heart chamber.
 17. Thesystem of claim 13, further including a remote programmer.
 18. Thesystem of claim 17, in which the remote programmer provides parametersto the means for classifying, for adjusting the classification of theintervals.
 19. The system of claim 7, in which the pattern recognitionmodule counts, among a first predetermined number of most recentfirst-second interval pairs, a second predetermined number of one ormore first-second interval pairs in which the first interval is in thefirst category and the second interval is in the second category. 20.The system of claim 7, in which the classification module is operable toclassify a first interval and a second interval of a first-secondinterval pair formed by the previous and current intervals, and in whichthe classification module is operable to: classify the first interval ofthe first-second interval pair into the first category if it is longerthan a first duration, and to classify the first interval into thesecond category if it is shorther than the first duration; and classifythe second interval of the first-second interval pair into the firstcategory if it is longer than a second duration, and to classify thesecond interval into the second category if it is shorter than thesecond duration.